added lock acquire system call

src/kernel/thread_manager.rs

@@ -236,6 +236,44 @@ impl ThreadManager {
         
     }
 
+
+    ///    Wait until the lock become free.  Checking the
+    ///	state of the lock (free or busy) and modify it must be done
+    ///	atomically, so we need to disable interrupts before checking
+    ///	the value of free.
+    ///
+    ///	Note that thread_manager::thread_seep assumes that interrupts are disabled
+    ///	when it is called.
+    ///
+    /// ### Parameters
+    /// - **id** id of the lock, stored in [`ObjAddr`], id given by user program thought exceptions
+    /// - **machine** the machine where the threads are executed
+    pub fn lock_acquire(&mut self, id: i32, machine: &mut Machine) -> Result<MachineOk, MachineError> {
+        match self.get_g_current_thread() {
+            Some(thread) => {
+                let rc_thread = Rc::clone(thread);
+                let lock = self.get_obj_addrs().search_lock(id);
+                match lock {
+                    Some(lock) => {
+                        let old_status = machine.interrupt.set_status(InterruptStatus::InterruptOff);
+                        if lock.free {
+                            lock.free = false;
+                            lock.owner = Some(Rc::clone(&rc_thread))
+                        } else {
+                            let thread = Rc::clone(&rc_thread);
+                            lock.waiting_queue.push(Rc::clone(&thread));
+                            self.thread_sleep(machine, Rc::clone(&thread));
+                        }
+                        machine.interrupt.set_status(old_status);
+                        Ok(MachineOk::Ok)
+                    },
+                    None => Err("Cannot find lock")?
+                }
+            },
+            None => unreachable!("Current thread should not be None")
+        }
+    }
+
     /// Currently running thread
     pub fn get_g_current_thread(&mut self) -> &Option<Rc<RefCell<Thread>>> {
         &self.g_current_thread